1. Field of the Invention
The present invention relates to a dynamic viscoelasticity measuring apparatus, which is aimed to improve so-called accuracy of data to be a true value.
2. Description of the Related Art
A dynamic viscoelasticity measuring apparatus (hereinafter, referred to as a DMA) is an apparatus in which distortion or stress changing (oscillating) with time is applied to a sample and the distortion or stress generated in the sample is measured, to thereby analyze mechanical properties of the sample. In many of the apparatus, the sample to be measured is fixed to a holder member. When temperature dependence of the sample is measured and thermal expansion of the sample occurs, because the fixing force of the holder member is larger than the thermal expansion force, there may occur a problem in that the sample is curved. To address the problem, there is known a viscoelasticity apparatus including two sample holder members that do not move in the direction of applying stress or distortion and hold both ends of the sample in such a manner that the sample can be expanded or contracted in the direction connecting both ends by elastic deformation of the sample holder members (see Japanese Patent Application Laid-open No. Hei 02-045731).
In the technology described in Japanese Patent Application Laid-open No. Hei 02-0457321, instead of fixing both ends of the sample in all directions, the ends of the sample are respectively held by individual two sample holder members, which can move in the direction connecting both ends of the sample. Thus, even if the sample has temperature dependence, an accurate calculation result can be obtained without restricting deformation in the direction due to temperature change and without changing the assumption of a sample shape (to be a rectangular solid or a cylindrical column) for calculating a complex elastic modulus. In a specific elasticity modulus measurement, a sine wave generated from a sine wave generator is transmitted to a force generator via an amplifier, and hence a stress in the direction substantially perpendicular to a sample surface of the sample is generated via a detection rod. The stress is detected by a detector fixed to a part of the detection rod, together with distortion generated in the sample. From correlation between the stress and the distortion, the complex elastic modulus is calculated. In calculation of the complex elastic modulus, a precondition and an important factor for calculation accuracy reside in that a sample shape is a rectangular solid or a cylindrical column. Here, in the measurement, heating adjustment is performed by a heating source equipped for adjustment of temperature condition. This heat is transferred to the sample via two sample holder members, a part of an elastic arm, a sample grasping chuck, and a part of the detection rod. As a result, the sample is expanded thermally. Therefore, in order to calculate the complex elastic modulus accurately as described above, it is necessary that the thermal expansion of the sample should occur only in the direction connecting both ends of the sample, and it is necessary to suppress a deformation in the direction (measuring direction) perpendicular to the above-mentioned direction so that the sample can maintain the rectangular solid shape or the cylindrical column shape.
The task described in the above-mentioned conventional technology is to divide the sample holder member into two members at both ends of the sample, and hence to absorb the thermal expansion force of the sample in the direction connecting both ends of the sample. Thus, it is aimed to suppress the deformation in the direction perpendicular to the above-mentioned direction, with the result that the accuracy of data is improved.
However, if the stiffness of the sample made of polymer material or the like due to expansion is smaller than the stiffness of the elastic arms in the direction connecting both ends of the sample, the distance between the sample holder members does not increase to such an extent corresponding to the expansion of the sample, and hence data accuracy is not improved. In particular, in the region exceeding a glass transition temperature Tg as illustrated in FIG. 6, as the thermal expansion of the sample increases in a discontinuous manner, the sample becomes softened, and the stiffness of the sample decreases. Therefore, the stiffness of the elastic arms becomes relatively large, and hence the elastic arms are not extended in the sample expansion direction for absorbing the thermal expansion of the sample. As a result, there is no absorption of the thermal expansion in the direction connecting both ends of the sample, and the sample cannot maintain its rectangular solid shape or cylindrical column shape any more and thus an undesirable deformation occurs. For example, the sample may be buckled as illustrated in FIG. 5A, or the sample may be bent between the sample holder member and the chuck as illustrated in FIG. 5B. Consequently, it becomes difficult to measure the elasticity modulus as intended, and the data accuracy is deteriorated.